fix: use term name for label instead of taxonomy slug in product attribtes.

[creative-andrew]

This pull request introduces improvements to how variation attributes are handled and resolved in the WooCommerce GraphQL integration. The key changes include adding a label field to variation attributes and simplifying the resolution logic for the label field.

Enhancements to variation attribute handling:

• includes/data/connection/class-variation-attribute-connection-resolver.php: Added a new label field to the variation attributes data array. This field is populated with the attribute's value or term name, depending on the context.

• includes/type/object/class-variation-attribute-type.php: Simplified the resolver for the label field in the GraphQL schema. The resolver now directly returns the label field from the source if it exists, or null otherwise.What does this implement/fix? Explain your changes.

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When asking for the "LABEL" of a term in product attributes, we are getting the taxonomy slug.

BEFORE

Notice how we are getting color as the label of green.

AFTER

Notice how we are getting Green as the label of green as it should be.